FIG. 2 is a close-up of FIG. 1 illustrating links 11 between the satellites within the constellation. These links 11 may be between satellites 10 belonging to one and the same orbital plane 25, in which case intra-plane links 21 are spoken of, or between satellites 10 belonging to adjacent orbital planes 25, which are referred to as inter-plane links 22. Each satellite is thus linked to a maximum of four satellites 10. In FIG. 2, if the direction of movement of the satellites is taken as a reference, a satellite 10 may be linked to the two neighbouring satellites following the same orbital plane in front of and behind it, and to the two neighbouring satellites following the adjacent orbital planes 25 to the right and to the left of the satellite 10.
In order to establish the links between them, certain satellites 10 comprise inter-satellite communication terminals employing radiofrequency technologies. These satellites 10 make use of antennas dedicated to intra-orbital plane communications 21 and inter-orbital plane communications 22. By way of illustration, FIG. 3 shows an example of one embodiment of a platform 30 of such a satellite known from the prior art. This platform comprises two mobile antennas 32 for the inter-plane links 22 and two antennas with low mobility 31 for the intra-plane links 21.
These inter-satellite links 11, when employing radiofrequency technology, pose multiple problems in the case of use within a polar or near-polar constellation. Certain problems occur in particular due to the fact that the azimuthal angle of an inter-plane link 22 varies constantly with latitude over the course of the orbit and that the speed of variation of the azimuthal angle increases substantially as the two satellites approach the pole. Other problems arise from the fact that it is necessary to avoid possible interference between all of the beams present at the pole. In practice, inter-orbital plane links 22 cannot be sustained at extreme latitudes, typically those latitudes higher than about 60° and lower than about −60°, and must therefore be broken. Inter-satellite communication terminals are placed and oriented so as to establish links with the satellite to the right or to the left (with respect to the direction of movement) and are capable of aiming in a given azimuthal angular sector corresponding to these latitudes. Communications between satellites in neighbouring orbital planes 25 are therefore no longer available beyond these latitude values when the satellites pass over the polar regions.
One consequence is that a new inter-plane connection 21 must be established after crossing the pole and that this connection is not made with the same satellite. Specifically, with reference to FIG. 4, considering a satellite 10 orbiting in the central orbital plane 25, this satellite 10 is linked to two other satellites 10 that are placed in neighbouring orbital planes 25 on either side of the central orbital plane 25. In the polar regions, the orbital planes 25 cross one another and the satellite 10 which was located to the right of the satellite in question (taking the direction of movement of the satellites as a reference and seen from above with respect to Earth) will be located to the left of the satellite in question after passing over the pole. The same applies for the satellite 10 which was located to the left before passing over the pole. As soon as the satellite 10 has crossed the polar region, i.e. its latitude is higher than about 60° or lower than about −60° depending on the pole crossed, the inter-satellite communication terminals re-establish the inter-orbital plane links 22 with the satellites 10 of the neighbouring orbital plane 25. However, each terminal re-establishes the link 22 with a different satellite 10 with respect to the moment at which said link 22 was broken. For example, the inter-satellite communication terminal that was positioned on the platform for connection with the satellite to the right before passing over the pole will have to re-establish the inter-plane link 22 with the new satellite that is located to its right and which was previously to its left. This makes the procedure somewhat more complicated, all the more so if these breaking and re-establishing operations have to be carried out twice per orbit.